The present invention relates to a method of improving adhesion and an adhesion improver used therefor. More particularly, the invention has an object to provide a novel means for improving adhesion between the surface of shaped articles of various kinds of plastic or metallic materials as the substrate and the cured surface film of a silicone, i.e. organopolysiloxane composition, formed on the substrate surface to impart excellent wearing resistance and other excellent properties of the silicone to the surface.
As is well known, it is widely practiced in the prior art to provide the surface of a shaped article of a plastic resin or a metal with a cured surface of a silicone to impart excellent surface properties inherent to the silicone material.
One of the problems in such a method of surface coating is that good adhesion cannot always be obtained between the substrate surface and the cured coating film of the silicone with few exceptions of several specific combinations of certain kinds of plastics and the silicones having very limited structures.
It is therefore eagerly desired to develop an efficient adhesion improver or a primer to solve the above described problem of poor adhesion between the substrate surface and the cured coating film of silicones. Various types of such adhesion improvers have been proposed hitherto including, for example, a primer comprising a polyalkylene imine and a trialkoxy silane containing an epoxy group as the main ingredients (see Japanese Patent Publication 54-28429); a primer comprising an epoxy resin and a trialkoxy silane containing an amino or imino group as the main ingredients (see Japanese Patent Publication No. 54-28430); a composition comprising a polyisocyanate and a transesterification product of a polyester or polyether polyol with an alkoxy silane (see Japanese Patent Publication No. 48-41697); a composition mainly composed of methyl methacrylate (see Japanese Patent Publication No. 50-39096 and Japanese Patent Kokai No. 52-138565); a primer composition mainly composed of an epoxyalkyl trialkoxy silane (see Japanese Patent Kokai No. 54-81378); an undercoating composition comprising a specific silane compound and an acid anhydride (see Japanese Patent Kokai No. 54-155229); a composition comprising a co-hydrolysis product of at least two kinds of silane compounds and an alkyl-etherified methylol melamine (see Japanese Patent Kokai No. 55-99930); and the like. Unfortunately, none of these prior art primers or adhesion improvers can impart sufficiently high adhesion, resistance against hot water, weathering resistance and the like desired properties to the silicone coating films on the substrate surface.
On the other hand, shaped articles of polycarbonate resins are expected to be widely used in a variety of applications by virtue of the good transparency and excellent impact resistance thereof although they suffer from the problems in connection with the surface properties that they are remarkably susceptible to scratches resulting in decreased transparency and that they are relatively weak against the attack of organic solvents so that application of a polycarbonate resin is limited for such reasons.
Needless to say, various attempts have been made to improve the surface properties of a shaped article of polycarbonate resins without adversely affecting the excellent properties inherently possessed by the polycarbonate resins. The investigations hitherto undertaken for the most promising method are directed to impart the surface of the polycarbonate resin articles with a cured surface coating film of an organopolysiloxane composition having excellent wearing resistance.
A problem in the above approach is that sufficiently good adhesion can not always be obtained between the surface of a polycarbonate resin article and the organopolysiloxane composition capable of forming a coating film having excellent wearing resistance.
Thus, there are known no means for effectively improving the surface properties of a shaped article of a plastic resin or, in particular, polycarbonate resin in respect of adhesion, weathering resistance, resistance against water or, in particular, hot water.